The present invention relates to a method and an apparatus for manufacturing superconducting compacted stranded wires with keystone angles.
A dipole magnet, which is disposed in an accelerator ring of a circular particle accelerator, is required to generate magnetic field of higher intensity and generate dipole magnetic field in the long distance. To satisfy these requirements, a saddle coil is frequently used as the dipole magnet for the accelerator. The saddle coil has a structure in which compacted stranded wires are placed along the axis of the coil and turned at both coil ends in sequence so as to form an arch shape as a whole, so that a cross section in the straight portion of the coil is shaped into a sector form. In order that a packing rate in a superconducting portion within the saddle coil is raised to obtain a high current density in the coil, it is desired to employ superconducting stranded wires of which cross section is shaped into a so-called keystone type. The keystone type superconducting compacted stranded wires 1xe2x80x2, formed from stranded wires comprising superconducting wires 2xe2x80x2, as shown in FIG. 7, is formed to have a trapezoidal-shaped cross-section which has two side ends of different heights, one side end 3xe2x80x2 shorter than the other side end 4xe2x80x2, as shown in FIG. 7.
Conventionally, in general, the keystone type compacted stranded wires are produced through procedures described in detail hereunder. A plurality of superconducting wires are stranded into stranded wires (hereinafter referred to as superconducting stranded wires). The superconducting wires are press-formed in four directions by four rolls, as shown in FIGS. 5A and 5B, thus producing compacted stranded wires of which cross section is trapezoidal. The four rolls are made up of, rolls 5xe2x80x2 and 6xe2x80x2 (hereinafter referred to as tapered rolls) and cylindrical rolls (hereinafter referred to as flat rolls) 7xe2x80x2 and 8xe2x80x2. The tapered rolls 5 and 6 have rotation axes parallel with each other and are tapered on the outer surface thereof, while the flat rolls 7xe2x80x2 and 8xe2x80x2 have rotation axes orthogonal to those of the tapered rolls 5xe2x80x2 and 6xe2x80x2.
The packing rate in the compacted stranded wires is set to be a high value so as to increase the current density in the coil. This setting causes the superconducting wires to locally receive higher compressive force and tension during being stranded. In particular, edge portions of the compacted stranded wires receive bending force, in addition to the above-mentioned compressive force and tension, so that the superconducting wires deform in such manner that the original shape thereof hardly remains.
When superconducting stranded wires are roll-formed to obtain a keystone angle, one side end portion of both side end portions of the superconducting compacted stranded wires, which is thinner than the other side end portion in the cross section, receives the most severe compressive force, Thus, breakage of superconducting filaments serving as transportation paths of current may occur. Furthermore, in roll-forming, some of the superconducting wires which have lost respective destination in a closed space enclosed between rolls and adjacent superconducting wires may extend excessively in its longitudinal direction, thus causing a locally reduced sectional area of the superconducting filaments. What is worse, the superconducting wires with no destination may cause burrs. It is therefore apt to cause some drawbacks in both of the superconducting properties and contours.
In cases the keystone type superconducting compacted stranded wires are manufactured in the industrial scale, the keystone angle is specified as being less than one degree. Burrs produced on the edge portions in one side end of the superconducting compacted stranded wires, which is thinner than the other side in the cross section, may be removed by grinding. Removing the burrs on the edge portions in such a way leads to partial removal of a normal conducting matrix disposed for stabilization. Therefore, there is a problem in which the stability in the superconducting property in the portion with the burrs removed is locally lowered. Furthermore, when the portion removed by grinding extends to superconducting filament portions, there occurs a problem in which the current to be transported is reduced in large extent.
A method of manufacturing keystone type superconducting compacted stranded wires according to the present invention is to roll-form superconducting stranded wires into keystone type superconducting compacted stranded wires by using a pair of tapered rolls of which outer surfaces are tapered and of which rotation axes are parallel with each other and a pair of flat rolls of which rotation axes are perpendicular to those of the tapered rolls and parallel with each other, one side of said superconducting stranded wires, which becomes thinner than other side of said superconducting stranded wires after being roll-formed, being contacted with one of said pair of flat rolls before said other side of said superconducting stranded wires is contacted with other of said pair of flat rolls.
An apparatus for manufacturing keystone type superconducting compacted stranded wires according to the present invention includes a group of forming rolls comprising a pair of tapered rolls of which rotation axes are parallel with each other and a pair of flat rolls of which rotation axes are parallel with each other and are orthogonal to the rotation axes of the tapered rolls, in which a diameter of one flat roll in said pair of flat rolls to contact with the one side of the superconducting stranded wires, which is thinner than the other side after being roll-formed, is larger than that of the other roll in said pair of flat rolls.
Superconducting stranded wires to be roll-formed according to the present invention includes superconducting stranded wires which are pre-formed as required.